causes of expenditure which exist in the animal after birth.3

A very clear description of the modern doctrine on this subject is given by Dr. Jeffray, in his Thesis de Placenta; a work which contains a judicious summary of the opinions that had been previously entertained upon the subject, together with many important original observations. We have some valuable remarks in Bichat; Anat. gen. t. i. p. 348; and Sur la Vie &c., p. 82. et seq.; mixed up, however, with much incorrect hypothesis, depending upon the metaphysical ideas which he enter tained respecting the relation between the vital functions. Mayow was quite aware of the degree in which the functions of the mother superseded those of the fœtus, p. 322; he limits the actions of the fœtus almost exclusively to the power of supporting its muscular contractility, and I may remark, that if an arterialized state of the blood be necessary for muscular contraction, it is essential that the fœtal blood should experience an equivalent change, to maintain the action of its heart. We have some judicious observations by Mr. Coleman on the state of the fœtal circulation, as connected with its other functions, Dissert. p. 46. et seq.; See also Legallois, Sur la Vie, p. 248, 9, on the fœtal functions. Dr. Edwards found the temperature of a seven months' child to be only 894°; De l'Influence &c. p. 236.

Since writing the above remarks, I have perused, in the last number of the Edinburgh Medical Journal, an account of the experiments of Dr. Williams, of Liverpool, the object of which is to prove the existence of a direct communication between the sanguiferous vessels of the mother and the fœtus. He operated upon dogs, and the plan which he pursued was to open a pregnant animal, immediately after it had been deprived of life, while the capillaries might still be supposed to retain their contractility, and to inject oil of turpentine coloured with alkanet root into the descending aorta. When the blood of the mother was supposed to be sufficiently impregnated with the oil, one of the pups was removed from the uterus, and its vessels

The state of the chick during incubation, although differing so considerably in its anatomical structure

being opened, a portion of the oil was found to have entered into them. It was detected either by suffering the blood of the fœtus to drop upon paper, to which it imparted a greasy stain, or the vessel was opened under water, in which case small globules of oil were observed floating upon the surface. Being in Liverpool in the autumn of 1824, in company with Dr. Roget, we were present at one of these experiments. This, however, as Dr. Williams candidly admits, was not successful, owing, in a great measure, as he supposed, to the size of the animal upon which he operated, being too large in proportion to the syringe and the quantity of injection which was employed. We also suggested that the result was liable to deception, in consequence of the peculiarly adhesive nature of the oil, which would cause it to adhere to the apparatus or the fingers of the operators, and might thus be accidentally smeared over the surface of the pup, or in some way interfere with the result. Dr. Williams has since endeavoured to obviate this objection by using rape oil, and by afterwards carefully washing the animal in an alkaline solution. An experiment is related, in which these precautions were employed, yet where the oil was still detected in the blood of the fœtus. The experiment is one which leads to such important conclusions, that I shall offer no apology to the author for making my remarks upon it without reserve. In the first place, the oil does not seem capable of penetrating into the vessels of the fœtus, unless it be employed in considerable quantity, and injected with considerable force; is there not therefore some reason to suspect that there may have been a rupture of the delicate cellular texture which is supposed to separate the maternal from the fatal vessels? 2d. Notwithstanding the care that was taken to wash off the oil, I conceive that it must be very difficult entirely to remove this cause of inaccuracy; it would therefore be desirable to employ some other substance, that is not liable to this objection, which might be dissolved or suspended in the blood of the mother and afterwards detected

and arrangements of the parts, physiologically considered, bears a close resemblance to the fœtus in utero. We have here an organ analogous to the placenta, in the form of a fine net-work of vessels distributed, on the external surface, of the contents of the egg, which receive the blood from the embryo in the venous and return it in the arterialized state, the shell being provided with a number of pores, which permit the air to act upon the blood, and thus enable it to undergo its appropriate change. Hence we find that a free access of air is as necessary to the evolution of the chick as to the existence of an animal with lungs, so that if the egg be completely

in that of the fœtus, by means of an appropriate chemical reagent. 3d. It seems to be agreed by all anatomists, and is admitted by Dr. Williams himself, that mercury cannot be made to pass from the mother to the fœtus, without an obvious extravasation taking place, a circumstance, which is at least a presumption against the existence of any natural passage, through which the oil could pass from one system of vessels to the other. 4th. It is known that when we draw off a large proportion of the blood of the mother, the quantity of blood in the fœtus does not appear to be diminished. 5th. The nature of the fœtal circulation, both as to the quantity of the blood, the rapidity of its motion, the number of its red particles and other properties are not what would seem to indicate that there is so very minute a channel of communication between the two sets of vessels, if we are to regard them as forming parts of the same circulating system. Should future experiments confirm those of Dr. Williams, the degree of effect would rather indicate some peculiar connexion, essential indeed to the existence of the fœtus, but different from the simple circulation of the blood, as it takes place in the other parts of the sanguiferous system.

smeared over with varnish, the chick is as effectually destroyed, as the animal after birth would be by submersion or suffocation.*

There is a subject connected with the effect of respiration on the living system, which must be noticed in this place, both as in itself sufficiently curious to demand our attention, and likewise because it has been supposed to throw light upon the theory of respiration, or upon the mode in which it affects the vital functions. I refer to the peculiar sensations which are experienced at great elevations. These sensations have been supposed to be connected with the action of the lungs, both because a change in the density of the air is the only circumstance to which they can, with any probability, be assigned, and because the respiration appears to be generally affected by any change of this kind to which the lungs are subjected. The effect produced by ascending high mountains was distinctly noticed by Boyle he ascribes it to the rarefaction of the air, but he

4 Blumenbach's Compar. Physiol. by Lawrence, p. 483; Paris on the Physiology of the Egg, Ann. Phil. v. ii. N. S. p. 2. et seq. As was remarked above, we are indebted to Mayow for the first clear conception of this subject, although on some minor points his opinion is probably not correct. Sir Ev. Home has given us a series of very interesting engravings, exhibiting the progressive changes which the egg undergoes during incubation; Phil. Trans. for 1822. p. 339. et seq. I must not omit to mention, that in two very elaborate articles in Rees's Cyclopædia, "Egg" and "Incubation," the doctrine maintained in the text, respecting the action of the air upon the blood of the chick in ovo, is controverted in all its parts.

does not satisfactorily explain how rarefied air should produce the feelings which are experienced." Haller," with his usual diligence, has collected accounts from various travellers who have ascended high mountains, but the result of their testimony seems to be adverse to the supposition that any peculiar or specific effect is produced in these situations from the state of the air. He also informs us that this was the case with himself, in his expeditions among the Alps; he farther observes, that in many parts of Switzerland, there are individuals permanently residing at very considerable elevations, without experiencing any inconvenience, and it may be added that this still more remarkably takes place in some parts of the E. Indies and S. America. It is also stated that no effects of an analogous kind have ever been noticed with respect to the different species of animals that are found in these regions. Haller is

s Works, i. 105, 6; iii. 374, 5. The individuals to whom he refers experienced affections of the stomach, as well as of the lungs. It is also noticed by Mead, who ascribes it to extreme rarity of the air, so that enough of it cannot be taken into the lungs to inflate them; Works, v. i. p. 181.

6 El. Phys. viii. 3. 7.

7 According to Lieut. Gerard, Marang, a large town on the Sutlej, is 8,500 feet above the level of the ocean, and Skipké 9,000 feet, Geol. Trans. v. i. N. S. p. 128, 9; the village of Misang 10,165 feet, Edin. Phil. Journ. v. x. p. 302, and Nako 11,550 feet; he farther states that fields are cultivated at an elevation of 13,000 feet; Brewster's Journ. of Science, v. i p. 41. et seq. The height of the city of Quito is said to be above 9,000 feet; Jameson's Miner. v. iii. p. 333.